Engine only running on 2 Cylinders.

Hawaiiguy1018

Recruit
Joined
May 25, 2023
Messages
1
Hello everyone. My buddy recently got a boat with a 1977 Johnson 70 Evinrude on it. Recently, the boat has been running okay out of water with muffs on, but dies when putting into gear on the water. My first thought was it’s running on 2 or less cylinders, so I check. Sure enough, chamber 3 is dead. I pulled the wire on 3 while boat was running, and no change in idle. So then I swapped 2 and 3’s wires and still the same problem. After that I swapped 2 and 3’s plugs, and 3 was still dead. I did a compression test on all 3. 1 was 132psi, 2 was 120 psi, and 3 was 132psi. I’m not very familiar with outboard engines so any help would be appreciated. Thanks for looking. Also attaching a video of cylinder 3 sparking when touched with pliers
 

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racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
36,032
You need 4 things for the motor to run.----Fuel-- , Compression, ---Crankcase compression----Spark at the right time.-----So inspect the bottom carburetor.---Check reed valves for #3 cylinder.----Look for holes in crankcase of #3 cylinder.----You only have 2 of the 4 at the moment for #3 cylinder.----Might replace plug boot on #3 as well.
 

Crosbyman

Rear Admiral
Joined
Nov 5, 2006
Messages
4,904
easiest is probably the carb.. it is an old style carb with even simpler orifices ( no long needles like shown in old carbs) for low and high speed.... easy to clean/inspect

with low experience your best best is to start by trying to clear gummed up orifices with a good blast of carb cleaner . just remove the cover bolts #26 &#35 and blast in some carb cleaner....it may help no garantee like a full carb job !!

if no change well you have to pull the carb and go the whole 9 yards with peeking inside the carb body for dried fuel . plugged side passage, plugged up low speed circuit under the dime size plug #5 on top etc... etc.. float adjustment stuck fule inlet needle #391685099669491.png

look for u-tubes to assist you
 

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Crosbyman

Rear Admiral
Joined
Nov 5, 2006
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4,904
see carb clean up ... remember yours has no needles just orifices the rest of the procedure is pretty much the same. for starter do not mess with the delicate orifice plugs other than a strong blast of carb cleaner followed by air blast ( a Dollar store keyboard spray can will do if you have no compressor). check the side channel#32 top half (in yellow above pic) leading to the top of the carb low speed chamber ..

 
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